Bipolar transistors constitute a well-known type of active transistor device wherein the device emitter, base and collector regions comprise appropriately doped semiconductor regions having direct physical contact in a base-emitter-collector configuration. The base, emitter and collector regions are appropriately biased with electronic voltages, and a voltage or current applied to the base in order to control the switching of the device. Bipolar devices provide many beneficial operating characteristics including high switching speed and high power handling capability. Bipolar transistors were for many years incorporated onto integrated circuits and used in a multitude of electronic devices from computers to consumer electronics. Bipolar transistors, however, suffer the disadvantage of requiring a relatively high operating power.
Metal oxide semiconductor transistors, and more particularly complementary MOS (CMOS) transistors, represent a relatively more recent transistor design wherein semiconductor drain and source regions are spaced by a semiconductor gate region, a voltage or current being applied to the gate to control the switching of the transistor. CMOS devices exhibit the desirable characteristic of requiring relatively low operating power in comparison to bipolar devices. Recent generations of CMOS devices have overcome various disadvantages including relatively large device size and relatively slow switching speeds in comparison to bipolar devices. However, CMOS devices are still relatively limited in their power-handling capabilities in comparison to bipolar devices.
Many electronic circuit applications require integrated circuits having both the ability to witch higher amounts of power and still operate using relatively lower power consumption. Such applications include mobile telephone electronics, automobile control electronics and multitudes of others know to the reader.
One form of integrated circuit, a bipolar-CMOS, or BiCMOS circuit, incorporates both bipolar and CMOS devices onto a single integrated circuit. See, for example, U.S. Pat. Nos. 5,256,582 and 5,181,095, both to Mosher et al., show a method of forming higher-power bipolar and lower-power MOS transistors on the same integrated circuit chip or substrate. With both bipolar and MOS devices incorporated onto a single integrated circuit, the bipolar transistors are used for higher-power switching and control applications while the MOS transistors are used for the lower-power logic applications.
One significant disadvantage of BiCMOS integrated circuits is that the processes of forming bipolar and CMOS devices are significantly different, requiring complex fabrication processes to form both types of devices on a single integrated circuit.
More recently attempts have been made to manufacture integrated circuits with CMOS devices having at least some portion thereof suitable for higher-power switching and control operations while the balance of the devices are suitable for high-speed, low-power logic applications. See, for example, U.S. Pat. No. 5,296,393 to Smayling et al. showing an insulated circuit including both complimentary CMOS logic devices and relatively higher-power insulated gate field-effect transistors (IGFETs). In some instances, however, IGFETs exhibit less than desirable operating characteristics, such as RDSon×Area.
The industry has recognized and the present inventors have similarly determined that it would be desirable to provide integrated circuits containing both CMOS devices operable as low-voltage logic devices and CMOS devices operable as relatively high-voltage switching and control devices. It would be further desirable if such processes and structures did not require complex variations to and deviations from ordinary CMOS manufacturing processes.